1. Field of the Invention
The present invention relates to golf shoes.
2. Description of the Related Art
Conventionally, golf shoes having a sole portion provided with a metal pin referred to as a spike pin have been in the mainstream. The spike pin sticks into the ground, thereby stabilizing the swing of a golf player. It is necessary to always maintain the spike pin perpendicularly to the ground surface and rocking is to be blocked during the swing. For this purpose, the sole portion is formed of a material having a high rigidity so that the spike pin is fixed firmly. In golf shoes, a clip plate for fixing the spike pin is to be buried in the sole portion. Therefore, the sole portion is much more rigid through the clip plate.
A large number of professional golf players and advanced amateur golf players (hereinafter referred to as xe2x80x9cadvanced golf playersxe2x80x9d) swing a golf club by effectively utilizing the sole portion having a high rigidity. In the take-back, the golf player effectively utilizes the inside edge of the sole portion for a kicking foot (a right foot for a right-handed golf player), thereby preventing the sway of his (her) weight. In the early stage of a down-swing, moreover, the golf player effectively utilizes the inside edge of the sole portion of the kicking foot to kick the ground and to transmit the force to a golf club. In the latter half of the down-swing, furthermore, the golf player effectively utilizes the outside edge of the sole portion for a pivoting foot (a left foot for the right-handed golf player) to stabilize the pivoting foot.
In recent years, so-called spikeless shoes comprising a sole portion provided with a projection formed of an elastic material such as synthetic resin or rubber in place of a spike pin have spread and have been the mainstream of the golf shoes. In the spikeless shoes, it is not necessary to firmly fix a spike pin. Therefore, it is not necessary to form the sole portion with a material having a high rigidity. However, the advanced golf player masters a swing form suitable for the sole portion having a high rigidity. In order to smoothly exchange the golf shoes having a spike pin with the spikeless shoes, the sole portion having a high rigidity is exactly utilized in the spikeless shoes.
The sole portion having a high rigidity is bent with difficulty during walking. Accordingly, when a golf player wearing the golf shoes comprising the sole portion walks for a long time, the feet are easily tired. A large number of unadvanced golf players (most of amateur golf players are not advanced) have low swing speeds. Therefore, the sole portion having a high rigidity gives small advantages. Under the actual circumstances, a large number of amateur golf players desire golf shoes having more walking easiness than swing easiness, that is, golf shoes excellent in a bending properties.
Japanese Unexamined Utility Model Publication No. Hei 6-17502 (1994/17502) has disclosed golf shoes comprising a sole portion in which a groove is formed. In the golf shoes, the bending property of the sole portion is enhanced by the groove formed except for the vicinity of a spike pin.
Also in such golf shoes, however, a clip plate for fixing the spike pin is buried in the sole portion. Accordingly, the bending property of the sole portion is still insufficient. If the groove is formed extremely deeply, the bending property is wholly enhanced. In this case, however, there is a possibility that the stability of a swing might be damaged.
The present invention has been made in consideration of such actual circumstances and has an object to provide golf shoes which give walking easiness and less fatigue and contribute to the stability of a swing.
In order to attain the object, the present invention provides a golf shoe comprising a sole portion and an upper portion and having a toe side flexibility evaluation value (Gt) of 0.0015 to 0.0100.
The golf shoe has a proper bending property. Accordingly, the suppression of a fatigue and the stability of a swing during walking are consistent with each other.
The toe side flexibility evaluation value (Gt) is calculated by the following equation (I).
Gt=(20/L)/Ftxe2x80x83xe2x80x83(I) 
In the equation (I), L represents an overall length (mm) of the sole portion. Furthermore, Ft represents a tensile load (N) required for fixing a half part of the sole portion close to a heel and pulling a front end close to a toe, thereby displacing the front end by 20 mm.
It is preferable that a heel side flexibility evaluation value (Gh) should be 0.0020 to 0.0090. During walking, consequently, the fatigue can be more suppressed and the swing can be more stabilized.
The heel side flexibility evaluation value (Gh) is calculated by the following equation (II).
Gh=(20/L)/Fhxe2x80x83xe2x80x83(II) 
In the equation (II), L represents an overall length (mm) of the sole portion. Furthermore, Fh represents a tensile load (N) required for fixing a half part of the sole portion close to the toe and pulling a rear end close to the heel, thereby displacing the rear end by 20 mm.
It is preferable that a ratio (Gt/Gh) of the toe side flexibility evaluation value (Gt) to the heel side flexibility evaluation value (Gh) should be 0.4 to 1.4. Consequently, the swing can be stabilized still more. Furthermore, the bending pattern of the golf shoe approximates to the natural bending pattern of a human foot and the fatigue can be suppressed still more during walking.
The present invention is particularly suitable for a golf shoe in which a sole portion is not provided with a pin formed of metal or ceramics but is provided with a projection formed of an elastic material.